1. Field of the Invention
The present invention relates to an anti-reflective layer (anti-reflective film) formed on the surface of a polymer molding material which reduces reflection in the visible light range and a production method thereof, and a stamper for forming the anti-reflective film and a production method thereof.
2. Description of Related Art
Polymer molding materials are widely used in various information equipment display devices. It is necessary to form an anti-reflective layer to inhibit reflected light to ensure satisfactory visibility. Multilayer films composed of dielectrics having different refractive indices are normally used as anti-reflective layers. Since vacuum deposition or sputtering is used to form the dielectric layer, there was the problem of requiring expensive devices and considerable production time to form the reflective layer.
On the other hand, a method for reducing reflectance is known in which a projections are imparted to the surface of the polymer molding material to form a layer in which reflectance continuously changes. A stamper having an arrangement of depressions corresponding to the projections is normally provided to impart the shape of the projections to the polymer molding material, and a method for processing the polymer molding material is employed using the stamper.
The depressions formed in the stamper for forming projections on the surface of the polymer molding material have an extremely low period as compared with the wavelength of light, and are required to have a depth of about ¼ the wavelength to adequately attenuate reflectance in the visible light range (see, for example, Japanese Unexamined Patent Application, First Publication No. 2003-43203). At this time, the depressions are required to have a tapered shape since they are required to cause reflectance to continuously change.
Electron beam lithography, or techniques combining patterning by optical exposure and semiconductor single crystal anisotropic etching exemplified by Si, are typically used to form an arrangement of depressions which satisfy such conditions. This involves forming openings at a desired period using various types of lithography, followed by forming tapered holes by wet or dry etching. Although electron beam lithography enables patterning at an adequate fine period for the lithography method, it requires considerable time and expensive equipment for processing. Although optical exposure methods employ a method in which a pattern is formed by utilizing the interference of laser light, it is difficult to form a structure having an adequate fine period.
A method has been proposed for forming a fine pattern which uses anodic oxidized porous alumina having a regular pore arrangement (see, for example, Kanamori et al., Appl. Phys. Lett., Vol. 78, No. 2, p. 142 (2001)). In this method, depressions are formed in an Si substrate by carrying out reactive ion etching using the anodic oxidized porous alumina having a regular pore arrangement as a mask. Although a technique for forming an arrangement of projections in a polymer can be easily surmised by using the similar arrangement of depressions formed in this manner as a mold, it is difficult to form a tapered shape required for the formation of a non-reflective layer with this method.
In addition, although a method has been proposed for carrying out etching on a porous structure of anodic oxidized porous alumina and producing a stamper based thereon (see, for example, Japanese Unexamined Patent Application, First Publication No. 2003-43203), since the shape of the pores of the anodic oxidized porous alumina is cylindrical, it is difficult to simply form projections having the controlled taper shape required for an anti-reflective film in a polymer molding material based thereon.